As shown in FIG. 10, a conventional turbo refrigeration unit 100 includes a centrifugal compressor 103, an oil-mist separation tank 102 that separates oil from a high-pressure gas refrigerant compressed by the centrifugal compressor 103, a condenser 105 that condenses the high-pressure gas refrigerant from which oil has been separated by the oil-mist separation tank 102, a high-stage expansion valve 107 that expands a high-pressure liquid refrigerant condensed by the condenser 105, an intercooler 106 that cools the liquid refrigerant expanded by the high-stage expansion valve 107, a low-stage expansion valve 108 that expands the liquid refrigerant cooled by the intercooler 106, an evaporator 109 that evaporates the low-pressure liquid refrigerant expanded by the low-stage expansion valve 108, and a gas-liquid separator 110 that separates the evaporated refrigerant into a gas refrigerant and a liquid refrigerant.
The centrifugal compressor 103 is rotationally driven by an electric motor 111 via a gear 101 to suction and compress the refrigerant. The high-pressure gas refrigerant compressed by the centrifugal compressor 103 reaches about 100° C., for example, and is guided to the oil-mist separation tank 102. From the high-pressure gas refrigerant guided to the oil-mist separation tank 102, oil is separated through centrifugal separation (for example, see PTLs (Patent Literatures) 1 to 4). The high-pressure gas refrigerant from which oil has been separated is guided to the shell-and-tube condenser 105, where it is subjected to heat exchange with heated water of 90° C., for example.
The high-pressure liquid refrigerant condensed in the condenser 105 through heat exchange with the heated water is expanded by passing through the high-stage expansion valve 107, which is provided at a downstream side of the condenser 105. The liquid refrigerant expanded by the high-stage expansion valve 107 is guided to the self-expansion-type intercooler 106.
Furthermore, a gas-phase part of the refrigerant guided to the intercooler 106 is guided to an intermediate stage of the centrifugal compressor 103.
The liquid refrigerant self-expanded in the intercooler 106 is guided to the low-stage expansion valve 108, where it is expanded. The expanded low-pressure liquid refrigerant is guided to the shell-and-tube evaporator 109, where it is evaporated through heat exchange with heat-source water of 40° C., for example. The refrigerant evaporated in the evaporator 109 is guided to the gas-liquid separator 110 and is separated into a gas refrigerant and a liquid refrigerant in the gas-liquid separator 110. The gas refrigerant obtained in the gas-liquid separator 110 is guided to the centrifugal compressor 103, where it is compressed.
Furthermore, part of the high-pressure gas refrigerant from which oil has been separated is guided from the oil-mist separation tank 102 to the gas-liquid separator 110 via a hot-gas bypass valve 112. The hot-gas bypass valve 112 controls the flow rate of the high-pressure gas refrigerant to be guided to the gas-liquid separator 110. The liquid refrigerant guided from a portion between the intercooler 106 and the low-stage expansion valve 108 merges at the downstream side of the hot-gas bypass valve 112 via a liquid injection valve 113. The liquid injection valve 113 controls the flow rate of the liquid refrigerant.
The high-pressure gas refrigerant that has passed through the hot-gas bypass valve 112 and the liquid refrigerant from the liquid injection valve 113 are injected into the gas-liquid separator 110. Thus, in the gas-liquid separator 110, the liquid refrigerant and the gas refrigerant whose temperatures are reduced to 40° C. to 50° C., for example, are separately obtained. In this way, by guiding the reduced-temperature gas refrigerant to an inlet of the centrifugal compressor 103, the load on the centrifugal compressor 103 is controlled.